Re: [ATM] Phase contrast and the 10 incher.

[Dominic-Luc Webb <dlwebb@canit.se>]

Sorry, sounds like we have some misunderstanding. I thought
this discussion was about surface irregularity in a coated
mirror as in some earlier discussions.

No problem! I see we are talking about two different mirrors;
one is coated and one is not. Sticking to the uncoated mirror
discussion, specifically so we are all looking at exactly same
thing:

http://home.comcast.net/~doeason/bvmirror/bvmirror.pdf

Dale specifies that he used optical glass cleaner. I can guess
this is something like dilute ammonia and alcohol. This would
not remove wax, tar etc. I could suggest a few tricks I have
used:

1)
Wash thoroughly using proper organic solvent (paint thinner, etc).

2)
Take pics from the side of this piece, preferably at different
angles, rather than just perpendicular. Rotate the mirror as well.

3)
Since this piece is clear, try placing sheet polarizers in same
orientation on either side.

4)
Sprinkle carbon dust over surface.

What these can tell you are whether these features are at
the surface (above or below) or inside the glass, whether
they reside on a single plane, or extend through different
depths, if there could be fractures, etc. If there are
fractures, their existance at or below the surface will
be revealed. This need not be a mystery. There are very
definitive ways to answer this.

Dominic

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